The present invention relates to fiber-optic transmission and to computer routers and servers, and, more particularly to a method and apparatus for a very high bandwidth analog or digital communications band source for use in fiber-optic data transmission applications or as very high bandwidth modulators for computer routers and servers.
At present, one of the important communications bands for optical fiber is at a wavelength of about 1.5 xcexcm. To get the most effective use of the bandwidth available in this band, a combination of direct modulation of 1.5 xcexcm sources and wavelength division multiplexing (WDM) are typically employed. The maximum modulation rate for standard products are about 10 Gb/s and there are now some special modulators available at about 40 Gb/s. It appears that the approaches used to get to 40 Gb/s will not be scalable to much higher frequencies for a number of reasons. So by using different optical wavelengths (i.e., WDM technology) together with high modulation rates (e.g., 10 Gb/s to 40 Gb/s as available today), a fair degree of the available fiber bandwidth can be used. However this approach has a number of drawbacks including: the requirement for multiplexing in a format which does not lend itself to packet switching (as is typical on the internet), multiplexing in a format which presents significant challenges for repeaters (as are required for long haul transmission), the cost of WDM systems tends to scale with the required throughput (this is contrary to the economic need for the cost to decrease as the usage increases), and there is a desire to use even more of the available bandwidth. Consequently it is desirable to be able to operate at still higher modulation rates.
Many of these issues also exist for data communications associated with future computer systems that will require greater than 40 GHz modulators, which is the upper range of today""s optical modulator technologies (e.g., integrated optics and electro-absorptive modulators).
These and other drawbacks and deficiencies of the prior art are overcome or alleviated by the present invention. A need exists to increase the amount of analog or digital information that can be transmitted over a communications channel such as a given optical fiber in fiber-optic communication applications or in future computer systems that will need to feed high data rate switches. Therefore, it would be desirable to have a method to directly modulate a 1.5 xcexcm wavelength source at higher rates. In the interest of clarity, the present invention is described with respect to the 1.5 xcexcm wavelength band, however the techniques described herein could also be employed at other fiber bands. WDM, or Dense Wavelength Division Multiplexing (DWDM), could then be applied to the result, with certain overlap restrictions.
A communications transmission system or light modulating system comprises a first source for providing terahertz (THz) radiation, a very large bandwidth modulator that imposes very large bandwidth information on the THz radiation, a second shorter wavelength source having an output wavelength suitable for transmission over fiber optic transmission systems, and a nonlinear optical conversion subsystem which imposes the THz modulated radiation onto the shorter wavelength transmission radiation to generate radiation suitable for transmission over a fiber optic communication system having the very large bandwidth information imposed on the resulting radiation to be transmitted through the optical fiber communication system or to ultra-fast switches used in ultra-fast computer servers and/or routers.
A method of increasing the amount of information transmitted over a communications channel and increasing the extinction ratio of a data transmission system comprises modulating a carrier signal having a first prescribed frequency with an information signal having a prescribed first bandwidth, generating thereby a modulated carrier signal having a second prescribed bandwidth; and mixing a transmission signal having a second prescribed frequency with the modulated carrier signal, generating thereby a converted transmission signal having a third prescribed bandwidth.
The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.